Cellulitis & Erysipelas: Diagnosis, Severity Grading, and Management

1. Diagnosis

Definitions

Cellulitis: Acute infection involving deep dermis and subcutaneous tissue.
Erysipelas: Acute infection involving the upper dermis and superficial lymphatics.

Etiology

Most common: Group A β-hemolytic streptococci (GAS).
Others: Staphylococcus aureus (MSSA, MRSA), Pasteurella multocida (animal bites), mixed flora in diabetic foot or chronic wounds.

Clinical Presentation

Feature	Erysipelas	Cellulitis
Onset	Abrupt	Gradual
Lesion Border	Raised, sharply demarcated	Flat, indistinct
Depth	Upper dermis + lymphatics	Deep dermis + subcutis
Color	Bright red	Pink–red
Systemic Symptoms	More frequent	Variable
Common Sites	Face, legs	Legs, arms, any break in skin

Positive Exam Findings

Localized erythema, warmth, swelling, tenderness.
Lymphangitic streaking.
Regional lymphadenopathy.

Negative Exam Findings

No fluctuance unless an abscess is present.
No crepitus or skin necrosis (these suggest necrotizing fasciitis).

2. Severity Grading (Based on IDSA)

Grade	Criteria	Example	Management Setting
Mild	Localized infection, no systemic signs	5×10 cm patch, afebrile, normal vitals	Outpatient
Moderate	Local infection + systemic signs (T >38°C, HR >90, RR >20, WBC >12K or <4K)	5×10 cm lesion with fever, tachycardia	May need IV antibiotics
Severe	Any of: Failed oral therapy, SIRS, hypotension, immunocompromised, rapidly progressive, concern for necrotizing infection	Expanding cellulitis with hypotension	Admit & urgent IV therapy

3. Management

General Principles

Control source: Treat entry portal (tinea pedis, trauma, ulcer).
Antibiotic selection: Target most likely pathogens.
Supportive measures: Limb elevation, analgesia, hydration.
Hospitalize if severe or complicated.

A. Mild Non-Purulent Cellulitis/Erysipelas

Likely pathogen: Streptococcus spp.

Oral options (Adults):
- Cephalexin 500 mg PO QID × 5–10 days.
- Penicillin V 500 mg PO QID × 5–10 days.
- Amoxicillin 500 mg PO TID × 5–10 days.
- Clindamycin 300–450 mg PO TID (penicillin-allergic).

Follow-up: Recheck within 48–72 hours.

B. Purulent Cellulitis or MRSA Risk

Likely pathogen: MRSA, MSSA.

Oral options:
- TMP–SMX (1–2 DS tabs PO BID) plus amoxicillin 500 mg PO TID.
- Doxycycline 100 mg PO BID plus amoxicillin.
- Clindamycin 300–450 mg PO TID (covers both strep & MRSA).

C. Moderate–Severe Infection

Likely pathogen: Streptococcus spp., MSSA, MRSA (if purulent).

IV options:
- Cefazolin 1–2 g IV q8h.
- Oxacillin / Cloxacillin 2 g IV q6h.
- Vancomycin (if MRSA risk).

Duration: 5–10 days, extend if slow to respond.

D. Special Situations

Animal/human bites, diabetic foot, polymicrobial risk:→ Amoxicillin–clavulanate 875/125 mg PO BID × 5–10 days.
Facial cellulitis from dental origin:→ Amoxicillin–clavulanate or IV ampicillin–sulbactam.
Severe immunocompromised:→ Broad-spectrum IV therapy pending cultures.

Supportive Care for All Grades

Elevate the affected limb above heart level.
Pain relief: Paracetamol 500–1000 mg q6h PRN; NSAIDs if no contraindication.
Hydration and nutrition support.
Mark margins of erythema for progression monitoring.

E. Indications for Surgical Consultation

Concern for necrotizing fasciitis (severe pain, rapid spread, skin necrosis, crepitus).
Abscess requiring incision and drainage.
Deep tissue involvement (fascia, muscle).

4. Complications to Monitor

Recurrent cellulitis → chronic lymphedema.
Abscess formation.
Sepsis.
Post-streptococcal glomerulonephritis (rare).

5. Patient Education

Importance of completing full antibiotic course.
Limb hygiene & moisturizing to prevent skin breaks.
Managing chronic edema with compression stockings if indicated.
Early presentation if recurrence or worsening symptoms.